Blood Biomarkers for Bone Fracture and Cartilage Injury

ABSTRACT

Blood biomarkers are described for use in methods and compositions to determine whether an individual has sustained a bone fracture or a cartilage injury.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/451,100 filed Oct. 23, 2009, which is a United States national stagefiling under 35 USC §371 of international application No.PCT/US2008/005463, filed Apr. 28, 2008, designating the US, which claimspriority to U.S. Provisional Application No. 60/926,316, filed Apr. 26,2007.

FIELD OF THE INVENTION

This invention is in the field of diagnosis of injuries. Morespecifically, the invention discloses means and methods for a rapid andaccurate detection of bone and cartilage injury in a human patient andother mammals based on the release into the peripheral circulation ofproteins involved with bone and cartilage repair.

BACKGROUND OF THE INVENTION

The blood of humans and other mammals is now known to be rich with alarge amount of previously unstudied molecules that could reflect theongoing physiologic state of various tissues. As blood flows throughmost of the tissues of the human body, the origins of plasma proteinsmay be diverse. The complex mixture of a blood plasma proteome from ahealthy human individual is expected to comprise well known bloodcomponent proteins such as albumin and other known proteins in arelatively high abundance and various other proteins that originate fromcirculating blood cells.

Bone normally undergoes continuous turnover and remodeling comprisingbone formation and bone resorption; two opposite and well balancedprocesses. A number of proteins related to this normal regenerativeprocess may be found in the plasma and/or urine of healthy individualsin amounts that are generally correlated with a relative decrease orincrease in bone turnover activity. See, e.g., Anderson et al., Mol.Cell. Proteomics, 1: 845-867 (2002). Following fracture, a large numberof growth factors, cytokines, and their cognate receptors involved inbone repair are highly expressed at the fracture site in the first hoursfollowing injury. Skeletal tissues are the main source of such proteins,while some are released from associated inflammatory cells at the siteof injury. See, e.g., Barnes et al., J. Bone Miner. Res., 14: 1805-1815(1999).

Injuries to bones and cartilage are routinely assessed and monitoredusing such well known standard methods such as X-rays, bone scans, andmagnetic resonance imaging (MRI). However, such methods typicallyrequire transporting a patient to a location that contains the machinerynecessary to carry out such analyses. Yet there are many situations inwhich it would be advantageous to be able to determine whether a patienthas sustained a bone fracture and/or cartilage injury without the needor benefit of X-ray, bone scan, or MRI studies. In addition, injuries tobone and cartilage are not always evident by such methods. Accordingly,needs remain for additional means and methods to detect and assess boneand cartilage injuries in patients.

SUMMARY OF THE INVENTION

The invention described herein solves the above problems by providing arapid and accurate method for detecting a bone fracture and cartilageinjuries in a human individual using a sample of the individual's blood.The invention is based on the discoveries that transforming growthfactor beta receptor III (TGFβrIII), which normally is not present inthe blood of a healthy human individual, appears in the peripheral bloodwhen a bone is fractured and that the level of cartilage acidic protein1 (CRTAC-1) is significantly elevated in the peripheral blood of anindividual that has an injury to cartilage. TGFβrIII and elevated levelsof CRTAC-1 continue to be detected in the blood for a period of time forat least 24 weeks after time of injury. Moreover, the detection ofTGFβrIII or of elevated levels of CRTAC-1 in the blood provides adiagnostic test for the presence of injury to bone or cartilage,respectively, that may be more sensitive than commonly employed methods,such as X-ray, bone scan, and magnetic resonance imaging (MRI), whichrequire specialized instruments. Furthermore, methods described hereincan be routinely carried out to monitor bone fracture or cartilageinjury in a patient. The methods described herein may be readily carriedout using any of a variety of formats.

A method described herein may be carried out on whole blood or afraction thereof, such as plasma or serum. Preferably, the plasmaportion of blood is used in the methods described herein.

In one embodiment, the invention provides a method of detecting afracture in a bone of a human individual in which a sample of blood isobtained from the human individual and assayed for the presence oftransforming growth factor beta receptor III (TGFβrIII), wherein thedetection of TGFβrIII in the blood sample indicates that the individualhas sustained a bone fracture.

Methods of detecting TGFβrIII and/or CRTAC-1 in a sample of bloodobtained from an individual according to the invention may also be usedto measure (quantitate) the level of TGFβrIII and/or CRTAC-1 present inthe sample of blood and thereby in the blood of the individual.

Since TGFβrIII is known to play a role in enhancing TGF-β signaltransduction in the process of bone formation (osteogenesis), thepresence of TGFβrIII in a sample of blood obtained from an individualmay also be used as an indication that the process of osteogenesis isstimulated in the individual. Likewise, because CRTAC-1 is a componentin the process of cartilage formation (chondrogenesis), thedetermination that there is an elevated level or an increasing level ofCRTAC-1 over time in one blood sample relative to another obtained froman individual may be used as an indication that the process ofchondrogenesis is stimulated in the individual.

In addition to methods for detecting whether an individual has sustainedan injury to bone or cartilage, the invention also provides methods thatmay be used to routinely monitor the time course of injury to bone orcartilage in an individual without the use of X-rays, bone scans, or MRIstudies. Such methods are especially useful in monitoring individualsthat may be at increased risk of bone fracture or cartilage injury, suchas an individual afflicted with osteoarthritis, osteoporosis, or agenetic disease that impairs osteogenesis or chondrogenesis, such asosteogenesis imperfecta (OI, “brittle bone disease”) in which the bonesof an individual are unusually brittle and susceptible to fracture. Suchmethods may also be used in monitoring an individual who may besuspected of having a bone or cartilage injury but is incapable ofeffective communication, such as infants; speaking impaired individuals;stroke patients; and patients in an altered consciousness state (ACS),such as coma, near coma, persistent vegetative state, vegetative state,or minimally conscious state. Such methods may also find use in theforensic analysis of injuries to an individual.

In another embodiment, the invention provides a method for monitoringthe state of a bone fracture in an individual comprising assaying forthe level of transforming growth factor beta receptor III (TGFβrIII) ina first blood sample and in a second blood sample, wherein the secondblood sample was obtained within two weeks, preferably one week,inclusive, after the first blood sample from the individual, andcomparing the level of TGFβrIII in the first blood sample with that ofthe second blood sample. In a further embodiment, a significant increasein the level of TGFβrIII of greater than about 20% or more between thefirst (earlier obtained) blood sample and the second (later obtained)blood sample indicates that the individual has sustained a bone fracturethat occurred within about 1 to about 2 weeks prior to the time of thesecond blood sample. In another embodiment, a decrease in the level ofTGFβrIII of greater than about 10% or more between the first bloodsample and the second blood sample indicates that the individual hassustained a bone fracture that occurred within about 2 to about 6 weeksprior to the time of the second blood sample. In yet another embodiment,where the level of TGFβrIII remains essentially steady, i.e., where thechange in the level of TGFβrIII between the first and second bloodsample is of about 6% or less, including no increase or decrease, thisindicates that the individual has sustained a bone fracture but hassustained no new bone fracture for at least about 6 weeks (morepreferably, within about 6 to about 24 weeks) prior to the time of thesecond blood sample.

In another embodiment, the invention provides a method of detecting acartilage injury in a human individual in which a sample of blood isobtained from the individual and assayed to determine the level ofcartilage acidic protein 1 (CRTAC-1) in the blood sample, wherein alevel of CRTAC-1 in the blood sample that is significantly higher, thatis, at least about 20% or more higher than the level previouslydetermined in a sample of blood from the individual indicates that theindividual has sustained a cartilage injury. Following a cartilageinjury in an individual, the level of CRTAC-1 in a blood sample of theindividual increases dramatically in the first weeks following theinjury, rising by at least about 40% (including as much as about 50%,about 60%, about 70%, about 80%, about 90%, and about 100%) higher thanthe level of CRTAC-1 in a blood sample from the individual prior to orat the time of the cartilage injury, or in comparison to a levelpreviously determined in a blood sample from the individual or to areference level or range of concentration for CRTAC-1 as determined froma healthy population of individuals not suffering from a cartilageinjury.

In another embodiment, the invention provides a method for monitoringthe state of a cartilage injury in an individual comprising assaying forthe level of cartilage acidic protein 1 (CRTAC-1) in a first bloodsample and in a second blood sample, wherein the second blood sample wasobtained from the individual within two weeks, preferably within a week,inclusive, of the first blood sample from the individual, and comparingthe level of CRTAC-1 in the first blood sample with that in the secondblood sample. In a further embodiment, an increase in the level ofCRTAC-1 of about 20% or more, more preferably about 24% or more, betweenthe first (earlier obtained) blood sample and the second (laterobtained) blood sample indicates that the individual has sustained acartilage injury that occurred within about 1 to about 2 weeks prior tothe time of the second blood sample. In still a further embodiment, adecrease in the level of CRTAC-1 of about 4.5% or more between the firstblood sample and the second blood sample indicates that the individualhas sustained a cartilage injury that occurred within about 6 to about10 weeks prior to the time of the second blood sample. In anotherembodiment, where the level of CRTAC-1 measured in the first and secondblood sample remains essentially steady, i.e., where the change in thelevel of CRTAC-1 is less than 2% between the first blood sample and thesecond blood sample, including no increase or decrease, indicates thatthe individual is in a steady state and has sustained no new cartilageinjury for at least about 10 weeks prior to the time of the second bloodsample.

Preferably, in a method described herein, a blood sample is assayedusing a binding partner that specifically binds TGRβrIII or CRTAC-1 asits cognate binding partner (cognate ligand). Binding partners includebinding proteins and aptamers. Binding proteins useful in the methodsand compositions described herein include, but are not limited to,full-length immunoglobulin antibody molecules comprising fourpolypeptide chains, i.e., two heavy (H) chains and two light (L) chains,wherein each pair of heavy and light chains forms an antigen bindingsite. Other binding proteins useful in the methods and compositionsdescribed herein include any of a variety of recombinant antibodyconstructs that possess an antigen binding site, including withoutlimitation, a functional antibody fragment, such a Fab, F(ab′)₂, and Fv;a hybrid antibody, such as a chimeric or humanized antibody; a singlechain antibody (scFv); a diabody; a dual-variable domain immunoglobulinmolecule; and the like. Such antibody binding proteins are especiallyadvantageous as they may be employed in any of a variety of immunoassayformats in which a blood sample of an individual is brought into contactwith an antibody binding protein for TGFβrIII and/or an antibody bindingprotein for CRTAC-1 under conditions suitable for the formation of abinding complex formed between the binding protein and the bindingpartner, which complex can then be detected using any of a varietymethods available in the art for detecting antibody/antigenimmunocomplexes.

A binding partner that binds TGFβrIII or CRTAC-1 may also have adetectable label (tag) or other molecule that permits detection of abinding complex formed between the binding partner and TGFβrIII orCRTAC-1 in a method described herein. Such detectable labels and othermolecules are well known in the art and include, without limitation,fluorescent labels, radiolabels, colorimetric molecules, affinity beads,and the like.

Formats used for immunoassays to detect antibody/antigen immunocomplexesmay also be employed in the methods and compositions described herein.Such formats for detecting or measuring the level of TGFβrIII or CRTAC-1in a sample of blood according to the invention include, but are notlimited to, enzyme linked immunoadsorbent assay (ELISA),immunoprecipitations, immunoblotting, affinity chromatography, assaystrips, dip sticks, and the like, wherein the blood sample is broughtinto contact with a binding protein for TGFβrIII or CRTAC-1 and theresulting binding complex detected.

In yet another embodiment, the invention provides a kit for detecting ormeasuring the level of TGFβrIII and/or CRTAC-1 in a sample of blood froman individual to determine if the individual has sustained a bonefracture or cartilage injury. Such kits may comprise a binding partnerfor TGFβrIII and/or CRTAC-1, one or more buffers or solutions forcarrying out the assay, and instructions that indicate how to use thekit to detect the presence of or measure the level of TGFβrIII and/orCRTAC-1 in a blood sample and to determine whether the individual hassustained a bone fracture or cartilage injury.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows graphs of the level (ng/ml) of transforming growth factorbeta receptor III (TGFβrIII) in blood samples (plasma) from patientsthat sustained a single traumatic fracture in the tibia as determinedwith 24 hours of injury and continuing for 24 weeks after injury asdescribed in Example 2, below. Diamonds indicate the average level ofTGFβrIII in blood samples from patients (n=26) in which the bonefracture healed over the course of 24 weeks following injury (“union”).Squares indicate the average level of TGFβrIII in blood samples frompatients (n=4) in which the fracture did not heal over the course of 24weeks following injury (“delayed union”). See description, infra, fordetails.

FIG. 2 shows graphs of the level (ng/ml) of cartilage acidic protein 1(CRTAC-1) in blood samples (plasma) from patients that sustained asingle fracture in the middle shaft or in the distal portion of thetibia without cartilage injury (“union”, “delayed union”) and in bloodsamples from patients that sustained a fracture in the middle shaft ofthe tibia and also a fracture in the distal portion extending into theankle joint with visible dislocation of the joint and damage to thecartilage layer (“cartilage damage”) as described in Example 2, below.Triangles indicate the average level of CRTAC-1 in blood samples frompatients (n=8) that sustained bone fractures and cartilage damage asdetermined over the course of 24 weeks following injury (“cartilagedamage”). Diamonds indicate the average level of CRTAC-1 in bloodsamples from patients (n=26) that sustained a bone fracture that healedover the course of the 24 weeks following injury (“union”). Squaresindicate the average level of CRTAC-1 in blood samples from patients(n=4) that sustained a bone fracture that did not heal over the courseof 24 weeks following injury (“delayed union”). See description, infra,for details.

DETAILED DESCRIPTION OF THE INVENTION

The invention is based on the discoveries that transforming growthfactor beta receptor III (TGFβrIII) appears in the peripheral blood ofhuman individuals that sustain a bone fracture and that elevated levelsof cartilage acidic protein 1 (CRTAC-1) appear in the peripheral bloodof human individuals that sustain cartilage injury. Neither TGFβrIII norCRTAC-1 was previously known to be released to the peripheralcirculation as the result of injury to bone or cartilage tissue. Thedetection of TGFβrIII and elevated levels of CRTAC-1 in the blood of anindividual may provide an even more sensitive indication of bonefracture and cartilage injury, respectively, than traditional diagnosticmethods such as X-rays and bone scans for bone fractures and magneticresonance imaging (MRI) for cartilage injury. Accordingly, TGFβrIII andCRTAC-1 are useful as blood biomarkers for bone fracture and cartilageinjury, respectively.

Methods described herein may also be used in assessing or monitoringinjury to bone and cartilage in individuals who are incapable ofeffective communication to a healthcare professional. Such individualmay include, but are not limited to, infants; speaking impairedindividuals; stroke patients; and patients in an altered consciousnessstate (ACS), such as coma, near coma, persistent vegetative state,vegetative state, or minimally conscious state. Methods described hereinmay also find use in the forensic analysis of injuries.

The methods and compositions of the present invention are contemplatedto be applied to the detection or measurement of either or both TGFβrIIIor CRTAC-1 in a sample of blood and are understood to encompass thedetection in whole blood or fractions thereof, such as plasma or serum.Particularly preferred is the use of blood plasma in the methods andcompositions described herein.

The methods and compositions of the present invention are especiallycontemplated to benefit human subjects, but they are suitable for anymammalian subject that expresses a TGFβrIII or a CRTAC-1.

In order that the invention may be more fully understood, the followterms are defined.

Unless indicated otherwise, when the terms “about” and “approximately”are used in combination with an amount, number, or value, then thatcombination describes the recited amount, number, or value alone as wellas the amount, number, or value plus or minus 10% of that amount,number, or value. By way of example, the phrases “about 40%” and“approximately 40%” disclose both “40%” and “from 36% to 44%,inclusive”.

A “binding partner” is any molecule, including any polypeptide,immunoglobulin, nucleic acid, or fragment thereof, which specificallybinds a cognate binding partner (cognate ligand) at one or more sites.Examples of binding partner/cognate ligand pairs includeantibody/antigen, receptor/ligand, biotin/streptavidin, andenzyme/substrate. A binding partner that is a polypeptide may also bereferred to as a “binding protein”. Binding partners useful in themethods and compositions described herein include antibody moleculesspecific for TGFβrIII or CRTAC-1. A binding partner that is a nucleicacid is referred to as an aptamer.

A “TGFβrIII binding partner” is any binding partner molecule, includingany polypeptide, immunoglobulin, or fragment thereof, which specificallybinds transforming growth factor beta receptor III (TGFβrIII) or anepitope thereof at one or more sites in the molecule.

A “CRTAC-1 binding partner” is any binding partner molecule, includingany polypeptide, immunoglobulin, or fragment thereof, which specificallybinds cartilage acidic protein 1 (CRTAC-1) or an epitope thereof at oneor more sites in the molecule.

A “TGFβrIII antibody” refers to a binding protein that contains at leastone antigen binding site that binds TGFβrIII or an epitope thereof.Similarly, a “CRTAC-1 antibody” refers to a binding protein thatcontains at least one antigen binding site that binds CRTAC-1 or anepitope thereof.

An “antibody” includes any of the classes of full-length mammalianimmunoglobulin classes (such as IgG, IgM, IgA, IgE, IgD) and subclassesthereof. An “antibody” may also be any fragment of a full-lengthimmunoglobulin that binds the same antigen, such a Fab, F(ab′)₂, and Fvfragments, as well as binding molecules that may be produced by proteinengineering or recombinant DNA technology, including but not limited to,a chimeric antibody, which comprises a binding domain or complementaritydetermining regions (CDRs) of an immunoglobulin fused or inserted intoanother immunoglobulin; a humanized antibody, which comprises the CDRsfrom a non-human antibody inserted into the framework of a humanantibody molecule; a single chain antibody (scFv); and a diabody (see,e.g., Holliger et al., Proc. Natl. Acad. Sci. USA, 90: 6444-6448(1993)).

An antibody useful in the methods and compositions described herein maybe monovalent, i.e., having a single binding site for binding a singleantigen (or epitope) molecule, or multivalent, i.e., having more thanone binding sites for binding more than one antigen (or epitope). Aclassic IgG antibody molecule has two antigen binding sites and, thus,is bivalent.

An antibody useful in the methods and compositions described herein maybe monospecific, i.e., binding a single type of antigen (or epitope), ormultispecific, i.e., binding two or more different antigens (orepitopes). A classic IgG antibody molecule that has two identicalantigen binding sites is thus monospecific with respect to the type ofantigen (or epitope) that it can bind. A bispecific antibody bindingpartner useful in the invention can bind at least one molecule ofTGFβrIII and at least one molecule of CRTAC-1. Bispecific antibodymolecules may be heterodimers of two halves of two different full-lengthimmunoglobulin molecules. For example, bispecific antibodies have beendescribed using “quadroma” technology that fuses two different hybridomacell lines, each capable of expressing a monoclonal antibody that bindsa different antigen. Random pairing of light and heavy chains of the twomonoclonal antibodies include heterodimers comprising a pair of heavyand light chains of one monoclonal antibody associated with a pair ofheavy and light chains of the other monoclonal antibody (see, e.g.,Milstein et al., Nature, 305: 537-540 (1983)). A variety of otherbispecific antibody molecules have been described using proteinengineering and recombinant DNA technology (see, e.g., Kriangkum et al.,Biomol. Eng., 18(2): 31-40 (2001)). Bispecific antibodies useful in theinvention may include, but are not limited to, bispecific diabodies(e.g., Holliger et al. (1993); Holliger et al., Cancer Immunol.Immunother., 45: 128-130 (1997); Wu et al., Immunotech., 2(1): 21-36(1996)), bispecific tandem scFv molecules, Fab mulitmers (see, e.g.,Miller et al, J. Immunol., 170: 4854-4861 (2003)), and dual variabledomain immunoglobulins (see, e.g., Wu et al., Nature Biotechnology,(Oct. 14, 2007)).

A composition or method described herein as “comprising” one or morenamed elements or steps is open-ended, meaning that the named elementsor steps are essential, but other elements or steps may be added withinthe scope of the composition or method. To avoid prolixity, it is alsounderstood that any composition or method described as “comprising” (orwhich “comprises”) one or more named elements or steps also describesthe corresponding, more limited composition or method “consistingessentially of” (or which “consists essentially of”) the same namedelements or steps, meaning that the composition or method includes thenamed essential elements or steps and may also include additionalelements or steps that do not materially affect the basic and novelcharacteristic(s) of the composition or method. It is also understoodthat any composition or method described herein as “comprising” or“consisting essentially of” one or more named elements or steps alsodescribes the corresponding, more limited, and closed-ended compositionor method “consisting of” (or “consists of”) the named elements or stepsto the exclusion of any other unnamed element or step. In anycomposition or method disclosed herein, known or disclosed equivalentsof any named essential element or step may be substituted for thatelement or step.

It is also understood that an element or step “selected from the groupconsisting of” refers to one or more of the elements or steps in thelist that follows, including combinations of any two or more of thelisted elements or steps.

The meanings of other terms will be evident to those skilled in the artincluding the meanings known in fields of orthopedic medicine, molecularbiology, immunology, and diagnostic methodologies.

Cartilage acidic protein 1 (CRTAC-1) is a glycosylated extracellularmatrix protein that has been isolated from human articular cartilagesecreted by chondrocytes. In cell culture, CRTAC-1 has been described asa candidate marker to distinguish the chondrocyte-like phenotype andactivity from osteoblast-like and mesenchymal stem cells (Steck et al.,Matrix Biol., 26: 30-41 (2007)).

Transforming growth factor beta receptor III (TGFβrIII) is known to beinvolved in developmental and regenerative processes. For example,TGFβrIII plays an essential role in murine and chick development, andTGFβrIII knockout mice have an embryonic lethal phenotype. TGFβrIIIfunctions as a co-receptor for TGF-β signal transduction by enhancingTGF-β binding to its receptor TGFβrII and thereby increasing TGF-βsignaling (see, e.g., Massague, J., Ann. Rev. Biochem., 67: 753-791(1998)). Enhancement of TGF-β signaling is important in bone fracturehealing wherein TGF-β1 and its receptor TGFβrII, together withextracellular matrix proteins osteocalcin and collagen type I, areinvolved in a coordinated manner to promote proper healing of bonefractures.

Transforming growth factor beta receptor III (TGFβrIII) and cartilageacidic protein 1 (CRTAC-1) have not previously been reported to be acomponent in the blood of humans. Both proteins were detected in plasmafrom human individuals that sustained long bone fractures (see, Example1, below). Further analysis revealed that TGFβrIII is normally not foundin the blood of healthy human individuals but is present in the blood ofindividuals who have sustained a bone fracture. In contrast, CRTAC-1 maybe found in the blood of healthy individuals but will be present atelevated levels in the peripheral blood in an individual that hassustained a cartilage injury. Moreover, the level of both proteins incirculating blood show a similar pattern of change in the weeksfollowing the injuries with which we have found them to be associated:the levels fluctuate between wide limits within the first ten weeksfollowing injury, first increasing significantly and precipitously inthe first 2 or 4 weeks (for TGFβrIII and CRTAC-1, respectively), thenfalling significantly over the next 6 weeks or so, then finally levelingoff to essentially a steady state, neither increasing nor decreasingsignificantly for 14 weeks or longer. See FIGS. 1 and 2.

According to the invention, a level of CRTAC-1 in a blood sample from ofan individual that is at least about 20% higher than a previouslydetermined level of CRTAC-1 in a sample of blood from the individual(i.e., a baseline level) or at least about 20% higher than an estimatedbaseline level from healthy (non-injured) individuals or historicalcontrols indicates that individual has sustained a cartilage injury.

According to the invention, a preferred method for detecting a bonefracture in a human individual comprises the steps of obtaining a sampleof blood from the human individual and assaying the sample of blood forthe presence of transforming growth factor beta receptor III (TGFβrIII),wherein the detection of TGFβrIII in the blood sample indicates that theindividual has sustained a fracture in a bone.

Any fracture of bone stimulates the process of bone formation, i.e.,osteogenesis, to regenerate bone and heal the fracture. Since TGFβrIIIis known to play a role in enhancing TGF-β signal transduction in theprocess of bone formation (osteogenesis), the presence of TGFβrIII in asample of blood obtained from an individual may also be used as anindication that osteogenesis has been stimulated in response to afracture. Likewise, because CRTAC-1 is a component in the process ofcartilage formation (chondrogenesis), the determination that the levelof CRTAC-1 in the blood of an individual is elevated may be used as anindication that the process of chondrogenesis has been stimulated inresponse to a cartilage injury.

Fractures in bone as detected by a method described herein may resultfrom any of a variety of conditions including, trauma and bone diseases.Metabolic bone diseases include, but are not limited to, osteoarthritis,osteoporosis, and osteogenesis imperfecta (OI, “brittle bone disease”).Fractures may occur in patients with osteoarthritis where a fullthickness defect in a joint so depletes the articular cartilage thatnormally cushions two opposing bones that the two bones make contact andgrind against one another and eventually fracture the surface of eitheror both of the opposing bones. Osteoporosis and OI are examples of bonediseases in which the bones of an individual are or can become unusuallybrittle and susceptible to fracture. For example, clinically undetectedfractures, such as microfractures, can occur in trabeculi withinvertebrae or in the proximal and distal metaphyseal areas of bones ofindividuals with osteoporosis. In the case of OI, bones can be sobrittle that relatively minor trauma (bumps) cause fractures that wouldnot normally occur in the bones of healthy individuals. Accordingly,testing a sample of peripheral blood for the presence of TGFβrIII asdescribed herein may be advantageously used to routinely monitor forbone fracture in a variety of patients without the need of equipment andtime involved in subjecting such patients to X-ray or bone scanprocedures. Moreover, methods described herein may indicate fracturesthat cannot be detected using conventional X-rays and bone scans, suchas microfractures and occluded fractures.

As described herein (see, Example 2, infra), a study of human patientswho have sustained a traumatic bone fracture has revealed that therelative level of transforming growth factor beta receptor III(TGFβrIII) in the blood of an individual over time provides usefulinformation regarding not only whether a fracture has occurred but thestate of bone fracture in an individual. Representative data are shownin the graphs of FIG. 1 in which the level of TGFβrIII as measured inblood samples from a population of bone fracture patients is followedover time. One of the graphs in FIG. 1 shows the level of TGFβrIII inblood samples from a portion of the patient population in which the bonefractures healed by 24 weeks from injury (“union”). The other graph inFIG. 1 shows the level of TGFβrIII in blood samples from the portion ofthe patient population in which the bone fractures did not heal by 24weeks from injury (“delayed union”). The data in FIG. 1 indicate thatfollowing fracture, the level of TGFβrIII in blood follows a relativelysteep rise within about 2 weeks following injury, followed by arelatively symmetrical steep decline within about a further 2 weeks,i.e., between about 2 weeks and about 4 weeks following fracture,followed by a slower rate of decline at about 4 weeks to about 6 weeksfollowing fracture, and, thereafter, from about 6 weeks out to about 24weeks following injury, there is an extended leveling off in the case offracture healing or a gradual rise in the case of delayed union.

Thus, another aspect of the invention is a method for monitoring thestate of a bone fracture in an individual comprising assaying for thelevel of transforming growth factor beta receptor III (TGFβrIII) in afirst blood sample and in a second blood sample, wherein the secondblood sample was obtained within two weeks, preferably within a week,inclusive, after the first blood sample from the individual, andcomparing the level of TGFβrIII in the first blood sample with that ofthe second blood sample. Moreover, an analysis of the representativedata provided in FIG. 1, permits a number of correlations to be madebetween the change in the level of TGFβrIII present in such a first(earlier obtained) blood sample and a second (later obtained) bloodsample with respect to the state of bone fracture in the individualincluding, but not limited to:

an increase in the level of TGFβrIII of at least about 20% or morebetween the first blood sample and the second blood sample indicatesthat the individual has sustained a bone fracture that occurred withinabout 1 to about 2 weeks prior to the time of the second blood sample;

a decrease in the level of TGFβrIII of at least about 10% or morebetween the first blood sample and the second blood sample indicatesthat the individual has sustained a bone fracture that occurred withinabout 2 to about 6 weeks prior to the time of the second blood sample;

a change in the level of TGFβrIII of about 6% or less, including no (0%)increase or decrease, indicates that the individual has sustained a bonefracture and has sustained no new bone fracture within about 6 weeks toabout 24 weeks prior to the time of the second blood sample.

Damage to cartilage may occur as the result of trauma or a progressivedisease that affects the cartilage tissue in joints or other parts ofthe body. For example, fractures to the distal portion of the tibia canextend into the ankle joint and damage the cartilage layer on thesurface of the calcanear bone and/or the distal tibial joint surface(see, Example 2, infra). Injuries to cartilage are typically detected bymagnetic resonance imaging (MRI). Clearly, an MRI can be useful in bothlocating a site of cartilage injury and assessing the particular damagethat has occurred in cartilage tissue. However, methods described hereinfor testing a blood sample for elevated levels of CRTAC-1 may be used todetermine if an individual has sustained a cartilage injury without theuse of an MRI. Moreover, methods described herein can be used todetermine whether an MRI study is even necessary. In particular, testinga sample of blood for an elevated level of expression of CRTAC-1 asdescribed herein is a convenient means for determining whether acartilage injury may even exist in an individual. Moreover, obtaining ablood sample to determine the level of CRTAC-1 as described herein maybe significantly less stressful for some individuals than beingsubjected to the constraint, noise, time, and expense involved inconducting an MRI study, especially if the analysis of the blood sampleindicates there is no cartilage injury so that an MRI procedure isunnecessary.

Methods described herein to determine whether an individual hassustained a cartilage injury may comprise the step of comparing a levelof CRTAC-1 in a blood sample from the individual with a reference levelor reference range of concentration of CRTAC-1 that is indicative of thelevel of CRTAC-1 present in the blood of healthy human individuals thatdo not have a cartilage injury. A reference level or referenceconcentration range of CRTAC-1 that is indicative of normal cartilagehealth may be obtained from a population of healthy individuals withnormal healthy cartilage tissue. The use of reference levels orreference ranges of concentrations for a blood biomarker is the basisfor virtually every biomarker currently used in blood tests to assessthe health of human patients. Accordingly, persons skilled in the art ofoptimizing diagnostic blood testing for use with respect to humanindividuals are familiar with the procedures for gathering andqualifying reference levels or concentration ranges of a particularbiomarker in the blood of a population of healthy individuals that wouldbe indicative of normal health (e.g., cartilage health) and the levelsof the biomarker that would indicate relevant injury, disease, orcondition (e.g., cartilage injury).

Alternatively, a method described herein may compare a level of CRTAC-1measured in a blood sample from an individual with one or more levels ofCRTAC-1 measured in one or more other blood samples that were obtainedfrom the same individual at a different point in time (earlier orlater). For example, testing the blood of an individual on a routinebasis to monitor the change in the level of CRTAC-1 present in the bloodover time, such as during periodic check-ups with a healthcareprofessional, is one way to provide a baseline CRTAC-1 level for anindividual. A pronounced increase in the level of CRTAC-1 from such abaseline level of CRTAC-1 indicates that the individual has sustained aninjury to cartilage tissue. Preferably, such a database for anindividual provides levels of CRTAC-1 in one or more prior blood samplesthat were obtained from the individual when the individual is considered(e.g., by a healthcare professional) to have healthy cartilage, i.e., tonot have sustained a cartilage injury.

A comparative study of levels of CRTAC-1 in blood from human patients isdescribed in Example 2 (infra). All patients in the study sustained atraumatic fracture in the tibia. A portion of the population of fracturepatients sustained a single fracture in the middle shaft or in thedistal portion of the tibia and no cartilage injury. Among thesepatients with a single fracture, a portion (“union”) healed over thecourse of 24 weeks after the time of injury (traumatic event). The otherportion (“delayed union”) failed to heal over the same 24 week posttrauma. Another group of patients (“cartilage damage”) sustained afracture in the distal portion of the tibia that extended into the anklejoint with a visible dislocation of the joint and damage to thecartilage layer on the surface of the calcanear bone and/or distaltibial joint surface and, thus, sustained a cartilage injury.

FIG. 2 shows graphs of the levels of CRTAC-1 in blood of patients in thethree groups in the comparative study over the course of 24 weeks fromthe time of injury. The levels of CRTAC-1 in blood from the patientswith a single fracture and no cartilage damage (“union” and “delayedunion”) serve as a control for the background fracture in the patientswith cartilage damage (“cartilage damage”). In the case of the “union”and “delayed union” groups in FIG. 2, the level of CRTAC-1 initiallyrose relatively steeply within about the first 2 weeks from the time ofinjury, followed by a period of more gradual rise for about another twoweeks, i.e., at about 2 to about 4 weeks from injury, and thereafter,leveled off or gradually declined over the course of about 4 to about 24weeks. In comparison, the level of CRTAC-1 in blood from the “cartilagedamage” group rose relatively steeply over the first 2 weeks from timeof injury, followed by a period of considerably slower increase orleveling off at about 2 to about 6 weeks from the time of injury,followed by a period of decline for about four weeks, i.e., at about 6to about 10 weeks, and thereafter, gradually declined and leveled offover the course of about 10 weeks to about 24 weeks from time of injuryuntil it reached the approximately same level or lower than firstmeasured after injury.

FIG. 2, shows that throughout the 24 week study, the level of CRTAC-1 inpatients with cartilage injury (“cartilage damage”) was always at leastabout 40% higher than the level of CRTAC-1 in blood from patientswithout cartilage injury (“union”, “delayed union”). Accordingly, in oneaspect of the invention, a level of CRTAC-1 in a sample of blood from anindividual indicates that the individual has sustained a cartilageinjury when the level of CRTAC-1 is at least approximately 40%(including, in order of increasing preference, at least about 50%, atleast about 60%, at least about 70%, at least about 80%, at least about90%, and at least about 100%) higher than a level of CRTAC-1 previouslydetermined in a sample of blood from the individual when the individualwas known to have healthy cartilage or known to not have sustained acartilage injury.

Another aspect of the invention is a method of monitoring the state of acartilage injury in an individual comprising assaying for the level ofcartilage acidic protein 1 (CRTAC-1) in a first blood sample and in asecond blood sample, wherein the second blood sample was obtained fromthe individual within two weeks, preferably within a week, inclusive, ofthe first blood sample from the individual, and comparing the level ofCRTAC-1 in the first blood sample with that in the second blood sample.Moreover, an analysis of the representative data provided in FIG. 2,permits a number of correlations to be made between the change in thelevel of CRTAC-1 present in such a first (earlier obtained) blood sampleand a second (later obtained) blood sample with respect to the state ofcartilage injury in the individual including, but not limited to:

an increase in the level of CRTAC-1 of at least about 20% or more (morepreferably at least about 24% or more), between the first blood sampleand the second blood sample indicates that the individual has sustaineda cartilage injury that occurred within about 1 to about 2 weeks priorto the time of the second blood sample;

a decrease in the level of CRTAC-1 of about 4.5% or more between thefirst blood sample and the second blood sample indicates that theindividual has sustained a cartilage injury that occurred within about 6to about 10 weeks prior to the time of the second blood sample;

a change (increase or decrease) in the level of CRTAC-1 of less than 2%between the first blood sample and the second blood sample indicatesthat the individual is in a steady state and has sustained no newcartilage injury for at least about 10 weeks prior to the time of thesecond blood sample.

The accuracy of correlating a level or a difference in level of TGFβrIIIor CRTAC-1 biomarkers in one or more blood samples obtained from anindividual with the presence of a bone fracture or cartilage injury orwith the state of bone fracture or cartilage injury in the individualwill improve to the extent that the assays used to measure levels ofTGFβrIII or CRTAC-1 biomarkers in blood samples are exactly repeated orcomparably as accurate as those used to produce the data in Example 2(infra) and FIG. 1 (for TGFβrIII) and FIG. 2 (for CRTAC-1). Furthermore,it will be obvious to practitioners that when monitoring the level ofTGFβrIII or CRTAC-1 biomarkers for determining the stage of recoveryfrom a bone or cartilage injury that the frequency of measurements willhave an impact on the accuracy of the method, i.e., with more frequentblood samples taken closer together increasing the ability to correctlydetermine the stage of an injury in a patient or the proximity to aninjury event. Yet practitioners will also recognize that measurements ofTGFβrIII and CRTAC-1 biomarkers in blood samples that are taken over anextremely short period of time may undercut the accuracy or significanceof the methods described herein. Therefore, a sufficient period of timemust pass between time points at which blood samples are taken to permitthe detection of a change in the level of a biomarker to become evident.Preferably, blood samples employed in methods described herein are nottaken more frequently than one per day.

Any of a variety of means for the detection of TGFβrIII and/or CRTAC-1in a sample of blood may be employed in the methods and compositionsdescribed herein, including detection using liquid chromatography andmass spectrometry. TGFβrIII or CRTAC-1 may also be detected in a sampleof blood from an individual by contacting the blood sample with abinding partner for TGFβrIII or a binding partner for CRTAC-1.

Most preferably, a binding partner used to detect TGFβrIII or CRTAC-1 isan antibody molecule. Antibodies may be obtained commercially orgenerated by various methods known in the art. An antibody may be apolyclonal antibody, a monoclonal antibody, or a recombinant antibodymolecule.

The use of an antibody molecules as the binding partner to detectTGFβrIII or CRTAC-1 is particularly advantageous as antibodies may beemployed in various formats and protocols known in the art for thedetection (immunodetection) and measurement (quantitation) of a targetantigen (TGFβrIII or CRTAC-1) in a sample. Such formats and protocolsfor the immunodetection or quantitation of TGFβrIII or CRTAC-1 in asample of blood may include, without limitation, enzyme linkedimmunoadsorbent assays (ELISAs), immunoblots (e.g., Western blots),immunoprecipitations, immunoaffinity chromatography, and dip sticks. Insuch formats and protocols, antibodies may be immobilized on the surfaceof a solid substrate, e.g., by adsorbing or linking the antibodies tothe surface of the substrate. Examples of immobilized antibodies on thesurface of a solid substrate may take any of a variety of forms known inthe art including, but not limited to, the surface of a magnetic orchromatographic matrix particle, the surface of the wells of amicrotiter assay plate, and the surface of pieces or sheets of a solidsubstrate material (e.g., plastic, nylon, wood, cellulose,nitrocellulose, cellulose acetate, glass, cotton, fiberglass, and thelike). Pieces of solid substrate material containing immobilizedantibody adsorbed may be used as assay strips (or dipsticks) that can bedipped into or otherwise brought into contact with a blood sample eithermanually or robotically and then removed to detect the presence of boundantigen.

Protocols in which an antibody or other binding partner are adsorbed orlinked to the surface of a substrate preferably include the pretreatmentof the antibody containing substrate with a protein mixture (e.g.,gelatin, bovine serum albumin, and the like) to block undesirednon-specific binding of molecules to the surface of the substrate.

An immunocomplex formed by the binding of an antibody to its cognateantigen may be directly detected by the presence of a detectable labelor tag molecule attached to the antibody or indirectly detected by theuse of another molecule, such as another antibody, which can in turn bedetected. Detectable labels for use with antibodies are well known inthe art and include, but are not limited to, fluorescent labels,radioactive labels, biotin and streptavidin (or avidin) based detectionsystems, bioluminescent labels, chemiluminescent labels, and enzymeslinked to an antibody that are capable of reacting with colorigenicsubstrates to produce a detectable signal. A signal generated by suchsystems may be readily detected visually or by an appropriate instrumentand in some cases quantified, e.g., by fluorimetry, epifluorescencemicroscopy, confocal scanning laser microscopy, a luminometer, or acolorimetric assay. Robotic instruments are also available that permitthe reading of multiple samples with minimal human intervention.

A sandwich assay is a type of indirect assay for an immunocomplex. Asandwich assay may use a first antibody (the capture antibody) that willbind to its cognate target antigen (e.g., TGFβrIII or CRTAC-1) in asample to form an immunocomplex. The sample containing the captureantibody may then be reacted with a second antibody molecule (thedetection antibody) that can bind to an epitope on the capture antibodyor to an epitope that may be available on the antigen in theimmunocomplex. The detection antibody may carry a detectable label orcomponent of a signal generation system available in the art. By way ofexample and without intending to limit the invention, a capture antibodymay be a murine IgG antibody to TGFβrIII or CRTAC-1, and the detectionantibody may be a goat anti-murine IgG antibody that is conjugated to adetectable fluorescent tag molecule.

The invention further contemplates a method for detecting or measuringthe level of TGFβrIII and the level of CRTAC-1 in peripheral blood of ahuman individual comprising the steps of obtaining a sample ofperipheral blood from the individual and assaying the sample of bloodfor the level of TGFβrIII and CRTAC-1. Preferably, the level TGFβrIIIand CRTAC-1 in the blood sample is determined by contacting the bloodsample with a binding partner for TGFβrIII and a binding partner forCRTAC-1. Depending on the format of the assay, the blood sample may bebrought into contact with each binding partner separately (i.e., inseparate assays), consecutively in the same assay, or simultaneously inthe same assay.

Materials necessary for detection of TGFβrIII or CRTAC-1 in a sample ofblood (or plasma or serum) are conveniently assembled into a kit, sothat personnel treating or transporting a trauma victim can determinequickly whether a bone fracture has been sustained by a patient. Apreferred kit of the invention comprises a first (capture) bindingpartner(s) for either or each of TGFβrIII or CRTAC-1 immobilized on asolid substrate material, such as an anti-TGFβrIII or anti-CRTAC-1antibody immobilized on an assay strip, the wells of a microtiter plate,or on beads or particles; a second (capture) binding partner that willbind the first binding partner and that contains a detectable label orcomponent to produce a detectable signal; and instructions that indicatehow to use the kit to carry out the assay to detect either or bothTGFβrIII and CRTAC-1 in a peripheral blood sample. Beads, assay strips,or microtiter plates containing immobilized first binding partnermolecules in kits of the invention may be packaged in a varietyconditions, including a dry, unhydrated state; a freeze-dried ordehydrated state; or a hydrated state in a physiological buffersolution. Kits may also contain a device for obtaining a sample of bloodfrom an individual (e.g., a syringe or small pin to obtain a few dropsof blood). Kits may also contain other solutions for washing, forblocking non-specific binding, or for signal generation may also beincluded in the kits of the invention. In a preferred embodiment, a kitof the invention comprises capture binding partner(s) immobilized on asolid substrate, such as a bead, an assay strip or a microtiter plate,which has also been pre-treated to prevent interference by non-specificbinding of molecules to the substrate.

The methods and compositions described herein may find use in rapiddiagnosis for bone or cartilage injury by emergency and medicalpersonnel or in the periodic monitoring of the condition of a bonefracture or cartilage injury. The nature of the methods and compositionsdescribed herein makes it possible to perform diagnosis and monitoringof bone and cartilage injuries in a variety of environments, includingambulances or other mobile medical facilities, laboratories, hospitals,emergency rooms, sanitoria, homes, and other private facilities.

Additional embodiments and features of the invention will be apparentfrom the following non-limiting examples.

EXAMPLES Example 1 Identification of Candidate Protein Biomarkers forBone and Cartilage Metabolism in Plasma from Human Patients with LongBone Fractures

In this study, samples of blood were drawn from human patients with anacute bone fracture and analyzed for expression of candidate biomarkersfor bone fracture and fracture healing. The plasma proteins of patientswere characterized by sodium dodecyl sulfate polyacrylamide gelelectrophoresis (SDS-PAGE) and affinity purification, followed by tandemmass spectrometry liquid chromatography (LC-MS/MS). LC-MS/MS providespicomolar level of detection of proteins expressed in the plasmasamples. Following identification of proteins expressed in the plasma ofthe fracture patients, those species that are associated with bone andcartilage metabolism were singled out for further analysis.

Materials and Methods Plasma Collection

Human blood plasma samples were supplied by the Clinic of Traumatologyin Zagreb, Croatia. The approval for the collecting samples was obtainedfrom the Ethics Committee of the same institution. Blood samples from 25adult humans with a single long bone fracture (21-60 years of age) weredrawn into syringes containing 3.8% sodium citrate to form ananticoagulant-to-blood ratio (v/v) 1:9. Plasma was obtained bycentrifugation (15 min at 3000×g), and aliquots of each adult bloodsample were pooled for the further analysis. Aliquot samples were storedat −80° C. until used.

Affinity Column Purification

Pooled plasma of patients with a single-bone fracture (80 ml) wasdiluted two-fold with 10 mM sodium phosphate buffer (pH 7), and appliedto a column of heparin Sepharose affinity chromatography matrix(Amersham Pharmacia Biotech), previously equilibrated with 10 mM sodiumphosphate buffer (pH 7). Bound proteins were eluted from the column with10 mM sodium phosphate buffer (pH 7) containing 1 M and 2 M NaCl. Elutedfractions were precipitated with saturated ammonium sulfate (SAS) tofinal concentration of 35%.

SDS-PAGE and In-Gel Digestion

Samples were run on a NUPAGE® 10% Bis-Tris SDS-PAGE system (Invitrogen,Carlsbad, Calif.) using MOPS SDS buffer system, and subsequently stainedwith Coomassie staining kit (NuPAGE, Invitrogen) followingmanufacturer's instructions. After staining, each of the seven gel laneswas sliced into 12 pieces, and the corresponding pieces were combined.The pieces were then subjected to in-gel reduction, alkylation, andtrypsin digestion as described previously (Grgurevic et al., J.Nephrol., 20: 311-319 (2007)). Gel pieces were washed two times withacetonitrile/25 mM NH₄HCO₃, reduced by incubation with 10 mMdithiothreitol (DTT) for 45 minutes at 56° C., andcarboxyamidomethylated by incubation in 55 mM iodoacetamide for 45minutes at room temperature. Trypsin (Promega) was added to dried gelpieces (150 ng per piece, diluted in 25 mM NH₄HCO₃) and incubatedovernight at 37° C. Tryptic peptides were extracted with formicacid/acetonitrile/H₂O (10:20:70); and 100% acetonitrile, dried andresuspended in trifluoroacetic acid/acetonitrile/H₂O (1:2:97) for MSanalysis.

Mass Spectrometry

Tryptic peptides were analyzed by liquid chromatography-massspectrometry (LC-MS). An Agilent 1100 nanoflow HPLC system (AgilentTechnologies) was coupled to a LTQ-Orbitrap mass spectrometer (ThermoScientific) using a nano-electrospray LC-MS interface (ProxeonBiosystems). Peptides were loaded on a home-made 75 μm C₁₈ HPLC columnin solvent “A” (0.5% acetic acid in Milli-Q water) and eluted with a70-minute segmented linear gradient of 10%-60% solvent “B” (80%acetonitrile, 0.5% acetic acid in Milli-Q water) at a flow rate of ca.250 nL/min. Mass spectrometer was operated in the positive ion mode.Each measurement cycle consisted of a full MS scan acquired in theorbitrap analyzer at a resolution of 60000, and MS/MS fragmentation ofthe five most-intense ions in the linear ion trap analyzer. To furtherimprove mass accuracy, the lock-mass option was used as describedpreviously (Olsen et al., Mol. Cell. Proteomics, 4: 2010-2021 (2005)).This resulted in a typical peptide average absolute mass accuracy ofless than 1 ppm.

Peak lists were generated using in-house developed software (Raw2 msm)(Olsen et al., 2005), and searched against concatenated forward andreverse (“decoy”) IPI human database (version 3.13) using Mascot searchengine (Matrix Science). Searches were done with trypsin specificity (2missed cleavages allowed), carboxyamidomethylation as fixedmodification, and oxidized methionine as variable modification.Precursor ion and fragment ion mass tolerances were 10 ppm and 0.5 Da,respectively. Results of the database search were validated in theMSQuant software (available from SOURECEFORGE.NET®). Only peptides witha mass deviation lower than 5 ppm were accepted; two peptides wererequired for protein identification. Gene ontology (GO) analysis wasperformed using ProteinCenter software package (Proxeon Biosystems).

Results

Pooled plasma samples were subjected to heparin affinity chromatographyto enrich for proteins specific for bone and cartilage, many of whichare known to have heparin binding domains. This also partially removedhighly abundant plasma proteins, such as albumin, immunoglobulins,transferin, and haptoglobulin. Fractions of interest were collected,precipitated, with ammonium sulfate and separated on one dimensionalSDS-PAGE gels. Gel bands were excised, digested with trypsin, andanalyzed by LC-MS/MS. Peptide fragmentation spectra were searchedagainst the human IPI protein database, and the results of the databasesearch were validated using MSQuant software. Only peptides with a massdeviation lower than 5 ppm were accepted; two peptides were required forprotein identification, which led to an overall false-positive rate ofless than 1% at both the peptide and the protein level.

In total, two hundred and thirteen nonredundant proteins were identifiedin the in-gel analysis of pooled plasma proteins from 25 patients with abone fracture. Gene ontology (GO) analysis of plasma proteins showedthat a majority (63.8%) of detected proteins were of extracellularorigin, whereas only a small number (7.5%) were of intracellular(cytosol and nucleus) origin. Interestingly, a relatively high number(35.2%) of membrane related proteins were also detected.

According to molecular function analysis, 37.6% of detected proteins hadcatalytic properties, 18.3% were classified as signal transducers, and13.1% as transporters.

In terms of biological activity, a significant proportion of detectedproteins were involved in cell growth and proliferation (21.1%),transport (23.9%) and coagulation (13.1%).

Identification of Bone- and Cartilage-Related Proteins

From the proteins initially identified by the methodology describedabove in the pooled plasma samples of individuals with a long bonefracture, the twelve proteins listed in Table 1, below, were consideredas having possible involvement in bone and cartilage metabolism.

TABLE 1 Proteins in Plasma of Bone Fracture Patients Related to Bone andCartilage Formation Previously GO console: Identified in Protein IPIAccession No. Molecular Function Plasma transforming growth 304865.3receptor activity No factor beta receptor III signal transducer(TGFβrIII) splice isoform 1 of 451624.1 metal ion binding No cartilageacidic protein 1 precursor (CRTAC-1) extracellular matrix 3351.2 signaltransducer Yes protein 1 precursor structural molecule transporteractivity transforming growth 18219.1 protein binding No factor betainduced protein IG-H3 precursor (TGFβ IG-H3) splice isoform 2 of220701.3 enzyme regulator activity Yes collagen alpha 3 (VI) proteinbinding chain precursor structural molecule type IV collagenase 27780.1catalytic activity Yes precursor enzyme regulator activity metal ionbinding alpha 3 type VI collagen 22200.2 enzyme regulator activity Noisoform 1 precursor protein binding structural molecule procollagen Cproteinase 299738.1 nucleic acid binding No enhancer protein proteinbinding precursor isoform long of collagen 22822.4 metal ion binding Yesalpha-1 (XVIII) chain protein binding precursor structural moleculehyaluron binding protein 41065.3 catalytic activity Yes 2 precursormetalloproteinase 32292.1 catalytic activity Yes inhibitor 1 precursorenzyme regulator metal ion binding splice isoform A of 24825.2 not knownYes proteoglycan-4 precursor

As noted in Table 1, above, among the twelve proteins considered to beinvolved in bone and cartilage metabolism, five were not previouslyidentified in plasma.

Cartilage acidic protein 1 (CRTAC-1) was identified for the first timein plasma with 28 peptides and an average peptide Mascot score of 53.

Transforming growth factor beta receptor III (TGFβrIII) was identifiedfor the first time in plasma with four specific peptides and an averageMascot score of 44.

Transforming growth factor beta induced protein IG-H3 (TGFβ-IG-H3) wasalso identified for the first time in plasma with 20 peptides and anaverage peptide Mascot score of 57.

Among extracellular matrix proteins which were not previously detectedin plasma was the alpha 3 type VI collagen isoform 1 identified with twopeptides and an average peptide Mascot score of 60.

Previously identified in plasma, the splice isoform A of theproteoglycan-4 (or lubricin) was identified with two peptides and anaverage peptide Mascot score of 60.

Extracellular matrix proteins previously identified in plasma included:isoform long of collagen alpha-1 (XVIII) chain precursor (or endostatin)identified with five peptides and an average Mascot score of 36, spliceisoform 2 of collagen alpha 3 (VI) chain precursor identified with tenpeptides and an average Mascot score of 62, extracellular matrix protein1 precursor identified with 57 peptides and an average Mascot score of54, and type IV collagenase precursor (or matrix metalloproteinase-2,MMP2) identified with three peptides and an average Mascot score of 74.MMP-2 degrades extra-cellular proteins and disrupts the subendothelialbasement membrane, thus enabling the transmigration of inflammatorycells. Metalloproteinase inhibitor 1 precursor (TIMP-1) was identifiedwith five peptides and an average peptide Mascot score of 49.

Example 2 Monitoring Plasma Levels of Transforming Growth Factor βReceptor III (TGFβrIII) as Blood Biomarker for Bone Fracture andCartilage Acidic Protein 1 (CRTAC-1) as Blood Biomarker for CartilageInjury

In this study, the blood of human patients who sustained an acute bonefracture was monitored for the presence of transforming growth factor βreceptor III (TGFβrIII) and cartilage acidic protein 1 (CRTAC-1).

Material and Methods Patients

Within 24 hours of injury, thirty (30) patients (24-67 years of age) whosustained a fracture of the tibia were enlisted in this study. Allpatients gave written informed consent, and the study procedures were inaccordance with the Ethics Committee of Clinics of Traumatology of theMedical School of Zagreb. The criterion for inclusion in the study wasthat a patient had a radiologically confirmed fracture in the middleshaft or in the distal portion of the tibia. An additional eight (8)patients had a fracture in the distal portion of the tibia that extendedinto the ankle joint with a visible dislocation of the joint and damageto the cartilage layer on the surface of the calcanear bone and/ordistal tibial joint surface as diagnosed by magnetic resonance imaging(MRI).

Venous Blood Samples

From all included patients, peripheral venous blood was drawn atperiodic intervals according to a standardized time pattern at day 1, 3,and 7 following injury, and then at 2, 6, 10, 14, 18, and 24 weeksfollowing fracture. If the fracture healing was delayed, the bloodsamples were collected periodically until bony consolidation wasachieved. Blood was drawn into syringes containing 3.8% sodium citrateto form an anticoagulant-to-blood ratio (v/v) 1:9. Plasma was obtainedby centrifugation (15 min at 3 000×g), and aliquots of plasma sampleswere stored at −80° C. until used.

Radiological Evaluation

Physical examinations and radiographs were completed to assess theevidence of a bone union. At 24 weeks after injury, fractures werepronounced as healed or as non-union by two independent radiologists.All patients underwent surgery to insert an interlocking nail into thefracture. X-rays were taken pre-operatively, immediatelypostoperatively, and then at regular bi-weekly intervals up to 24 weeksfollowing surgery. X-rays were taken in two positions, i.e., ananterio-posterior view and a latero-lateral view. A fracture waspronounced as healed when all four cortices healed. However, partialhealing was graded when one, two, or three cortices rebridged.Additional injury of the calcanear or distal tibial joint cartilage wasconfirmed by MRI.

Measurement of TGFβrIII and CRTAC-1 in Blood Plasma

An enzyme-linked immunoadsorbent assay (ELISA) was developed to measureblood concentrations of TGFβrIII and CRTAC-1 in plasma from patientthroughout the follow-up (24 week) period. Polyclonal antibodies wereraised in rabbits immunized with specific human peptides of TGFβrIII andCRTAC-1 by standard methods. A monoclonal antibody against TGFβrIII waspurchased from Santa Cruz (A-4: sc-74511-mouse monoclonal antibody). Allsamples from 30 patients were measured twice, and a mean value was thenincluded in the final median range.

The ELISA for TGFβrIII specifically detects the biologically activesoluble form of the TGFβrIII in human plasma with a sensitivity of 10pg/ml. The minimal detectable dose of TGFβrIII ranged from 5.5 to 35pg/ml.

The ELISA for CRTAC-1 in human plasma provided measurable levels ofCRTAC-1 within a range of 10.5 to 55 pg/ml.

Formation of Cross-Linked Antibody-Protein G Complex andImmunoprecipitation

Rabbit polycloncal antibody (Genera Research Laboratory) against thesoluble form of TGFβrIII or against CRTAC-1 was incubated with protein Gagarose beads for 15 minutes on a shaker. The antibody-protein G beadsamples were centrifuged for 2 minutes on 12,000×g, and the supernatantsremoved. Formalin (500 μl of 4% formalin) was then added to the pelletand incubated for another 30 minutes on the shaker. The samples werecentrifuged for 2 minutes on 12,000×g, and the supernatants removed. Theresulting pellets (antibody cross-linked to protein G beads) wereresuspended in a phosphate-buffered saline (PBS) and added to collectedplasma samples for immunoprecipitation of cognate antigen, i.e.,TGFβrIII or CRTAC-1.

The mixtures of plasma samples and antibody cross-linked beads wereincubated overnight to allow formation of immunocomplexes betweenantigen (TGFβrIII or CRTAC-1) in the plasma samples and the antibodycross-linked beads. The samples were then centrifuged for 2 minutes on12,000×g to obtain pellets comprising immunocomplexes formed betweenTGFβrIII or CRTAC-1 and antibody cross-linked beads. The supernatantswere removed, and the pellets were washed three times with aphosphate-buffered saline and prepared for gel electrophoresis.

Gel Electrophoresis and Western Immunoblotting

Aliquots of samples were analyzed by electrophoresis and immunoblottingin a Novex mini-gel electrophoresis system. Gel electrophoresis samplebuffer was added to each pellet. The samples were denatured by heatingat 99° C. for 3 minutes followed by centrifugation for 2 minutes on12,000×g. Supernatants were then analyzed on a 10% polyacrylamide/SDSgel (Invitrogen). After electrophoresis, proteins in the gels weretransferred by electroblotting to nitrocellulose membranes and incubatedfirst with rabbit antibody against TGFβrIII and rabbit antibody againstCRTAC-1. The bound antibodies were detected with alkalinephosphatase-conjugated anti-rabbit IgG immunoglobulin (immunodetectionkit, Invitrogen).

Results

Physical examinations and radiographs were completed to assess theevidence of a bone union in patients. At 24 weeks after injury, 26fractures were pronounced as healed by two independent radiologists,while four (4) patients had non-union fractures. Six patients had anadditional injury of the joint cartilage based on MRI analysis.

Reference Values

The postoperative TGFβrIII reference level in plasma of patients withnormal fracture healing was 30.6±7.5 ng/ml (15-47 ng/ml). The level ofTGFβrIII in plasma of patients with delayed union was 32.4±8.2 ng/ml(18-52 ng/ml) without a significant difference (P=0.861).

The plasma concentration of CRTAC-1 in patients with normal fracturehealing was in the range of 50.4±9.1 ng/ml. In patients with a delayedunion fracture, the value was 51.2±5.3 ng/ml. Plasma concentrations ofCRTAC-1 in patients with an additional joint cartilage injury was83.4±7.8 ng/ml (67-112 ng/ml), which was significantly higher than inpatients without a joint cartilage injury (P<0.01, Wilcoxon test).

Time Courses

Levels of transforming growth factor β receptor III (TGFβrIII) in plasmaof patients with a bone fracture that healed (“union”) and in plasma ofpatients with a bone fracture that did not heal (“delayed union”) overthe course of 24 weeks following injury are shown in Table 2, below.

TABLE 2 Plasma Levels of TGFβrIII in Patients with Bone Fracture WeekAfter TGFβrIII TGFβrIII Injury (union*, ng/ml) (delayed union^(‡),ng/ml) 1 32.3 31 2 45.4 40 4 28 20 6 26 15 10 32.5 15.5 14 33.4 17 1832.7 17.8 24 33.1 21 *“union” refers to patients with a bone fracturethat healed within 24 weeks of injury; ^(‡)“delayed union” refers topatients with a bone fracture that did not heal within 24 weeks ofinjury

As can be seen from a graph of the data in Table 2 (FIG. 1), in patientswith normal bone fracture healing (“union”) as well as in patients withdelayed bone fracture healing (“delayed union”), TGFβrIII plasmaconcentrations reached their highest values at week 2 following injury.After the second week, TGFβrIII plasma levels declined in patients withdelayed union, and at 5 weeks following injury, TGFβrIII concentrationswere below the reference level of this group of patients. In patientswith a normal fracture healing (“union” in FIG. 1), TGFβrIII plasmaconcentrations also decreased after the second week following injury.However, the plasma value did not fall below the reference level, andslightly increased at 10 weeks following injury. Thereafter, the leveldid not change towards the end of the follow up period. See, FIG. 1.These data indicate that TGFβrIII is particularly useful as a bloodbiomarker for detecting bone fracture.

With respect to the quantitative levels of TGFβrIII in the blood samplesof the patients, the data in FIG. 1 indicate that if the level ofTGFβrIII falls below 20 ng/ml after week 4, then there is a possibilitythat a delayed union or non-union fracture has developed. The data inFIG. 1 also indicate that the maintenance of blood levels of TGFβrIIIabove 25 ng/ml after week 4 reflects a normal healing process asconfirmed by X-rays and clinical exam and a high probability that thebone will fully regenerate by week 24.

Table 3, below, shows the levels of cartilage acidic protein 1 (CRTAC-1)in plasma of patients with a bone fracture that healed (“union”), inplasma of patients with a bone fracture that did not heal (“delayedunion”), and in plasma of patients that sustained a bone fracture and anarticular cartilage injury (“cartilage damage”) over the course of 24weeks following injury.

TABLE 3 Plasma Levels of CRTAC-1 in Patients with Bone Fractures andCartilage Injuries Week Plasma CRTAC-1 Plasma CRTAC-1 CRTAC-1 After(union*, (delayed nion^(‡), (cartilage damage^(†), Injury ng/ml) ng/ml)ng/ml) 1 42 46 78 2 55 53 97 4 58 55 100 6 56 50 98 10 54 48 80 14 55 4978 18 50 47 76 24 48 46 76 *“union” refers to patients with bonefracture that healed within 24 weeks of injury; ^(‡)“delayed union”refers to patients with bone fracture did not heal within 24 weeks ofinjury; ^(†)“cartilage damage” refers to patients that sustained bonefracture and cartilage injury

As can be seen from a graph of the data in Table 3 (FIG. 2), in patientsthat sustained a bone fracture and also damage to articular cartilage(“cartilage damage”), the concentration of CRTAC-1 in the blood rosewithin a week of injury and persisted at a level that was clearly higherthan the level of CRTAC-1 in the blood of patients that sustained a bonefracture without articular cartilage damage, whether the fracture healed(“union”) or did not heal (“delayed union”) within 24 weeks followinginjury. These data indicate that CRTAC-1 is useful as a blood biomarkerfor cartilage injury.

All publications, patent applications, patents, and other documentscited herein are incorporated by reference in their entirety. In case ofconflict, the present specification, including definitions, willcontrol. In addition, the materials, methods, and examples areillustrative only and not intended to be limiting.

Other variations and embodiments of the invention described herein willnow be apparent to those skilled in the art, and all such variants andalternative embodiments of the invention are intended to be encompassedwithin the foregoing description and the claims that follow.

1. A method of detecting an injury to cartilage in a human individualcomprising measuring the level of cartilage acidic protein 1 (CRTAC-1)in a first blood sample obtained from a first individual and comparingthe level of CRTAC-1 in the first blood sample to the level of CRTAC-1determined in a second blood sample from the first individual or asecond individual when the first or second individual did not have acartilage injury, wherein a level of CRTAC-1 in the first blood samplethat is at least about 20% higher than the level of CRTAC-1 in thesecond blood sample indicates that the first individual has sustained acartilage injury.
 2. The method according to claim 1, wherein the stepof measuring the level of CRTAC-1 in the first blood sample comprisescontacting the first blood sample with a binding partner for CRTAC-1 toform a binding complex between the binding partner and CRTAC-1 presentin the first blood sample.
 3. The method according to claim 2, whereinthe binding complex formed between the binding partner and CRTAC-1present in the first blood sample is detected by a detectable labelpresent on the binding partner.
 4. The method according to claim 2,wherein the binding complex formed between the binding partner andCRTAC-1 present in the first blood sample is detected by adding anantibody that binds to said binding partner or that binds to saidCRTAC-1 present in said binding complex and detecting said antibody by adetectable label present on said antibody.
 5. The method according toany one of claims 2-4, wherein the binding partner for CRTAC-1 is abinding protein or an aptamer that binds CRTAC-1.
 6. The methodaccording to claim 5, wherein said binding protein for CRTAC-1 is anantibody to CRTAC-1.
 7. A method of monitoring the state of a cartilageinjury in an individual comprising measuring the level of cartilageacidic protein 1 (CRTAC-1) in a first blood sample previously obtainedfrom the individual and comparing the level of CRTAC-1 in the firstblood sample with the level of CRTAC-1 measured in a second bloodsample, wherein the second blood sample was obtained within two weeks,inclusive, after the first blood sample from the individual, anddetermining whether the level of CRTAC-1 in the second blood sample hasincreased, decreased, or remained the same relative to the level in thefirst blood sample.
 8. A method for determining the time proximity of anindividual from a cartilage injury comprising: (a) obtaining a bloodsample from said individual at a first time point, (b) obtaining atleast one additional blood sample from said individual at a later timepoint, (c) determining the concentration of cartilage acidic protein 1(CRTAC-1) in at least said first blood sample and said at least oneadditional blood sample, wherein said first time point and said latertime point are within two weeks of each other, wherein a determinationthat an increase in CRTAC-1 concentration of at least about 20% hasoccurred between said first time point and said later time pointindicates that the individual has suffered a cartilage injury within twoweeks prior to said later time point, wherein a determination that adecrease in CRTAC-1 concentration of at least about 4.5% has occurredbetween said first time point and said later time point indicates thatthe individual has suffered a cartilage injury more than six weeks butless than ten weeks prior to said later time point, wherein adetermination that the concentration of CRTAC-1 has neither increased ordecreased more than about 2% between said first time point and saidlater time point indicates that the individual has not suffered acartilage injury for at least ten weeks prior to said later time point.9. The method according to claim 8, wherein said first time point andsaid at later time point are within one week of each other.
 10. A kitfor use in measuring the level of cartilage acidic protein 1 (CRTAC-1)in a blood sample previously obtained from an individual to determinewhether said individual has sustained a cartilage injury comprising: abinding partner that binds to cartilage acidic protein 1 (CRTAC-1); anantibody that binds the binding partner when the binding partner isbound to CRTAC-1; instructions for using the kit to measure the level ofCRTAC-1 in a blood sample previously obtained from an individual todetermine if said individual has sustained a cartilage injury.
 11. A kitfor use in detecting the presence of transforming growth factor betareceptor III (TGFβrIII) in a blood sample previously obtained from anindividual to determine whether said individual has sustained a bonefracture comprising: a binding partner that binds to transforming growthfactor beta receptor III (TGFβrIII); an antibody that binds the bindingpartner when the binding partner is bound to TGFβrIII; instructions forusing the kit to detect TGFβrIII in a blood sample previously obtainedfrom an individual to determine if said individual has sustained a bonefracture.
 12. The kit according to claim 10 or claim 11, furthercomprising a device to obtain a sample of blood from an individual.